The process of population increase and patterns of resource utilization of two spider mites, Oligonychus ununguis (Jacobi) and Panonychus citri (McGregor), under experimental conditions (Acari: Tetranychidae)

Abstract

SummaryPattern of population growth and characteristics of habitat utilization and of migration by two species of spider mites were studied under experimental conditions. The population growth of Oligonychus ununguis (Jacobi) on a chestnut occurred only on a single mite‐release leaf over a long period, and few individuals moved away. Most of the 2nd progeny generation females of this species emigrated from the mite‐release leaf as well as the sapling by means of ballooning threads. During this growth period, population density on the mite‐release leaf levelled off, whereas that on the sapling increased. In contrast, the foundress of Panonychus citri (McGregor) on citrus actively moved over several neighbouring leaves, and until the 2nd progeny generation females emerged, individuals were distributed over all the sapling leaves by means of walking. Emigration from the sapling was not observed until the 2nd progeny females emerged, and after that the mites emigrated by means of ballooning threads. The population density of P. citri on the sapling levelled off and was rather decreased on the mite‐release leaf at the time of mite emigration. Comparing the changing pattern of the relative degree of aggregation (m*/m) measured in two different units between these two species, the pattern of m*/m in 1 cm2 on the mite release leaf in O. ununguis resembled that of the unit of leaves on the sapling in P. citri. This result as well as behavioural observations indicate that migration of O. ununguis is the movement from leaf to leaf and that of P. citri from sapling to sapling. It is, therefore, concluded that the boundary of the microhabitat is a single leaf for O. ununguis but sapling or foliage for P. citri.